I have the EF-M 22 on order but am looking for another lens us use in low light situations. The 50mm f1.8 is popular but I just think it is a bit long (80mm FF). The 40 mm is very small and light (4.6 oz) and would fit in as a good lens for M cameras. Is there enough of an aperture advantage over the 18-150 (not sure what it's aperture is at 40mm) to make it worth while?